Problem 433. jogging?

Imagine x-y coordinate system and you are at the origin and your partner is on the x-axis at some small distance (d) away from you. You and your partner started jogging simultaneously, left foot first. You and your partner maintained identical rate of steps per second (r) and length of every step (s). Your track and your partner's track are parallel but at angle alpha to x-axis. Please note that alpha is less than 90 degrees. At the initial moment of starting your partner appeared to be ahead of you due to the angle alpha not being 90 degrees. After you finished jogging a long distance, a photograph of your foot prints at a random location looked as if your partner was neither behind nor ahead of you. Please calculate the largest alpha (degrees) possible under these constraints.